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JDBC and Relational Databases

Unable to Retrieve values

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Posts: 56

posted 10 years ago

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These are my two files to enter data into database and retrieve data from database.
I am able to enter the data into database but not able to retrieve the data from database.
What may be the reason ?? What is my mistake ?
Can anybody help me ?? Waiting for kind reply.
Thank you in advance.

HTML File

java file

import java.io.*;
import java.sql.*;

import javax.servlet.*;
import javax.servlet.http.*;

public class DataInsertTable extends HttpServlet
{
	public void doGet(HttpServletRequest req, HttpServletResponse res)
		throws IOException, ServletException
		{
		
			res.setContentType("text/html");
			PrintWriter pw = res.getWriter();
			
			PreparedStatement ps;
			Statement st = null;
			ResultSet rs = null;

try{

String nm = req.getParameter("name");
				String roll = req.getParameter("roll");
				String clas = req.getParameter("clas");
				String mono = req.getParameter("mono");

//				System.out.println("partik");

try	{
					Class.forName("oracle.jdbc.driver.OracleDriver");
				}
				catch(ClassNotFoundException ex) {
					System.out.println("driver not loaded");
					System.exit(1);

//	 			   ex.printStackTrace();
//				   System.out.println(ex);
				}
			
				String URL = "jdbc:oracle:thin:@192.168.106.87:1521:ORA11G";			
				String Username = "fuel_db";
				String Password = "foel";

Connection con = DriverManager.getConnection(URL,Username,Password);

//				System.out.println("partik");
				
				ps = con.prepareStatement("INSERT INTO student (name, rollno, class, mobileno) VALUES (?, ?, ?, ?)");
				ps.setString(1,nm);
				ps.setString(2,roll);
				ps.setString(3,clas);
				ps.setString(4,mono);

int i = ps.executeUpdate();

pw.println(i);

if(i!=0)	{
					pw.println("Your data has been stored in the database");
				}
				else	{
					pw.println("Your data could not be stored in the database");
				}
			}
			catch(Exception e)
			{
				pw.println(e.getMessage());
			}

try {
				rs = st.executeQuery("SELECT * FROM student");
				} catch (SQLException e) {
				e.getMessage();
				System.out.println("Error" +e);
			}
		
			try {
				while (rs.next()) {
				pw.println("<br>" + rs.getString(1) + ",\t "  + rs.getInt(2) + ",\t "  + rs.getString(3) + ",\t " + rs.getInt(4));
				}
		} catch (SQLException e) {
			e.getMessage();
			System.out.println("Error" +e);
		}
			try {
				rs.close();
			} catch (SQLException e) {
				e.getMessage();
				System.out.println("Error" +e);
			}
			try {
				st.close();
			} catch (SQLException e) {
				e.getMessage();
				System.out.println("Error" +e);

}
	} 
}

bala nannaka

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Posts: 49

posted 10 years ago

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PreparedStatement ps;
Statement st = null;
ResultSet rs = null;

rs = st.executeQuery("SELECT * FROM student");
} catch (SQLException e) {

The statement is not initalized so you will get null pointer exception.

try to use con.createStatement to initalize the statment

rajnish patel

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Posts: 56

posted 10 years ago

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bala nannaka wrote:

PreparedStatement ps;
Statement st = null;
ResultSet rs = null;

rs = st.executeQuery("SELECT * FROM student");
} catch (SQLException e) {

The statement is not initalized so you will get null pointer exception.

try to use con.createStatement to initalize the statment

Can you please explain me ??
(please give that portion of coding for me also.)
As I am abeginner I want to know the reason for getting Nullpointer exception in this.
So please explain me or give me any link so that I can learn from that.

by the way, thank you so much for reply.

rajnish patel

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Posts: 56

posted 10 years ago

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Either con.createstatement is not working for me or I dont know how to add it..

Please help me to do that.

asr chowdary

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Posts: 35

posted 10 years ago

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Hi

before this line " rs = st.executeQuery("SELECT * FROM student"); " can you add

st=con.createStatement();

then it will work.

Thanks

rajnish patel

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Posts: 56

posted 10 years ago

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Suresh babua wrote:Hi

before this line " rs = st.executeQuery("SELECT * FROM student"); " can you add

st=con.createStatement();

then it will work.

Thanks

Thank you so much. Problem is solved.

Thank you all of above who helped me.

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